Projection exposure apparatus

ABSTRACT

A projection exposure apparatus includes an illumination optical system for illuminating a pattern formed on a first object, with light, a projection optical system for projecting the pattern of the first object, illuminated by the illumination optical system, onto a second object for exposure of the same with the pattern, a main system including the illumination optical system and the projection optical system, and an interferometer for use in measurement of an optical characteristic of the projection optical system and being mounted on the main system.

This application is a divisional application of U.S. patent applicationSer. No. 09/533,377, filed Mar. 22, 2000, now U.S. Pat. No. 6,633,362.

FIELD OF THE INVENTION AND RELATED ART

This invention relates to a projection exposure apparatus forsemiconductor manufacture and, more particularly, to a projectionexposure apparatus for semiconductor manufacture which is usable in alithographic process for the production of semiconductor devices orliquid crystal display devices, for example.

The density of an integrated circuit is increasing, and thus, projectionexposure apparatuses for semiconductor manufacture should have a veryhigh resolving power for projection exposure of a wafer to a circuitpattern formed on a reticle. In projection optical systems of suchprojection exposure apparatuses, for improvement of the resolution, thenumerical aperture (NA) has been enlarged or light of shorterwavelengths has been used. At present, with a projection exposureapparatus having a light source of a KrF excimer laser (λ=248 nm) and NAof 0.6, a resolution of 0.18 micron is attainable.

Recently, super-resolution exposure techniques based on modifiedillumination such as ring-zone illumination or quadrupole illuminationhave been proposed. A resolution of 0.15-0.1 micron may be attainablewith them.

For production of a high resolution projection optical system, it isnecessary to perform precise adjustment after a projection opticalsystem is assembled. More specifically, for a projection optical system,optical evaluations in regard to spherical aberration, coma, distortion,and exposure magnification, for example, should be done. While adjustinglens group spacings or eccentricities, the optical performance thatsatisfies predetermined specifications is pursued. Usually, theevaluation of optical performance is made by projecting and printing animage of a mask pattern upon a resist (photosensitive material) appliedto a photosensitive substrate (wafer) and by observing, afterdevelopment, a resist image formed thereon.

As an alternative method, there is a method in which wavefrontaberration of a projection optical system is measured by use of aninterferometer. However, this method requires use of a specialapparatus.

As described above, in projection exposure apparatuses, it is necessaryto check the quality of a resist image for final lens performanceadjustment of a projection optical system. However, this procedureinvolves very complicated processes such as printing a pattern on aresist-coated wafer, developing the wafer, and observing a resist imageby use of a scan type electron microscope (SEM).

Additionally, since, after the optical adjustment and evaluation, aprojection optical system should be mounted on a projection exposureapparatus with its lenses and lens groups held fixed so that theperformance does not change, it is very difficult to adjust a projectionexposure optical system once the projection optical system isincorporated into the projection exposure apparatus. Practically,however, in wafer exposure processes, the projection optical system isinfluenced by irradiation with illumination light and the imageperformance thereof changes thereby.

Conventional projection exposure apparatuses are not equipped with anyeffective means for measuring wavefront aberration of a projectionoptical system after the same is mounted on the projection exposureapparatus. The goal for re-adjustment for image performance is,therefore, unfixed, and usually, the operation is interrupted tosuppress the change.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide aprojection exposure apparatus by which measurement of image performanceof a projection optical system, being mounted on the projection exposureapparatus, can be done easily.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a projection exposure apparatus accordingto a first embodiment of the present invention.

FIG. 2 is a schematic view of a projection exposure apparatus accordingto a second embodiment of the present invention.

FIG. 3 is a schematic view of a projection exposure apparatus accordingto a third embodiment of the present invention.

FIG. 4 is a schematic view of a projection exposure apparatus accordingto a fourth embodiment of the present invention.

FIG. 5 is a schematic view of a projection exposure apparatus accordingto a fifth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In some preferred embodiments of the present invention to be describedbelow, a main assembly of a projection exposure apparatus is equippedwith an interferometer for measurement of an optical performance of aprojection optical system, by which wavefront measurement for theprojection optical system can be done directly upon the main assembly ofthe projection exposure apparatus.

FIG. 1 is a schematic view of a projection exposure apparatus accordingto a first embodiment of the present invention. In this embodiment, theinvention is applied to an excimer laser stepper having an exposurewavelength of 248 nm.

Denoted in the drawing at 1 is a KrF excimer laser which is a lightsource for exposure (lithography). Light emitted from the light source 1enters a beam shaping optical system 2 by which it is shaped into a beamshape being symmetrical with respect to an optical axis. Through anincoherency transforming unit 3, the coherent length of the light isreduced. Then, the light goes through an illumination optical system 4,and it illuminates a reticle 15. The reticle 15 has a desired patternformed thereon. The reticle pattern is then projected by a projectionoptical system 16 and is imaged at a position 17. Denoted at 18 is achuck for carrying a wafer thereon. It is fixedly mounted on a stage. Inaddition to these components, the projection exposure apparatus includesan alignment detection optical system, a focus detection system and soon, all constituting a main system. They are not illustrated in FIG. 1,for simplification of the illustration.

Next, the structure of an interferometer for measurement of thewavefront of a projection optical system, will be described. Here, thearrangement shown in FIG. 1 is an example wherein a Fizeau typeinterferometer is provided at the reticle side.

In a case where the exposure light source comprises an excimer laser,usually, the coherent length is about several tens of millimeters,whereas the total length of a projection optical system, which is thesubject of measurement, is about 1,000 millimeters. For this reason, itis practically unable to provide a Fizeau type interferometer. Inconsideration of it, in this embodiment, a light source separate fromthe exposure light source is used exclusively for an interferometer formeasurement of the wavefront of the projection optical system.

Denoted in the drawing at 6 is the light source to be used exclusivelywith the interferometer. Since the exposure wavelength is 248 nm in thisembodiment, a light beam of 248 nm, corresponding to a second harmonicof an Ar laser is used. The Ar laser beam goes via a mirror and thenthrough a condenser system 7 and a pinhole 8. By means of a collimatorlens 9, the laser beam is transformed into a parallel beam. The diameterof the pinhole 8 is set as approximately the same as an Airy discdetermined by the numerical aperture of the collimator lens 9.Therefore, the light beam emitted from the pinhole 8 comprises asubstantially idealistically spherical wave. Since the collimator lens 9is designed and produced substantially free from aberration, it can beconsidered that the light emitted from the collimator lens 9 comprisesan idealistically plane wave. In the structure of FIG. 1, the light fromthe light source 1 may be guided to the pinhole 8 by use of apolarization plane preserving fiber.

The thus produced parallel beam goes via a half mirror 10 and a mirror11, and it enters a lens 12 which is what can be called a TS lens(Fizeau lens) wherein the final face functions as a reference surface.The mirror 11 and the lens 12 are held by an X-Y-Z stage 5.

Usually, steppers include a reticle-to-wafer aligning means which maycomprise a TTR alignment scope for detecting the wafer position throughthe reticle, and such an alignment scope may be mounted on and held by amoving mechanism for moving the TTR alignment scope to a desiredposition on the reticle. In this embodiment, such a TTR alignment scopeis used also as the interferometer objective lens 12 described above.

The interferometer objective lens 12 should be retracted out of the pathof exposure light of the projection optical system 16 in the exposureprocess, while on the other hand, it should be moved onto the light pathof the projection optical system for measurement of the wavefrontaberration. When the TTR alignment scope is used as the detectionoptical system as described, since the TTR alignment scope can be movedto any desired position upon a reticle, wavefront measurement can bedone with respect to plural points on the picture field in the exposureregion.

The curvature radius of the final face of the objective lens 12, at thereticle side thereof, is equal to the distance to the position 15 whichis equivalent to the pattern surface of the reticle. Thus, reflectionlight from that final face is directed, as reference light, to a lightreceiving surface of a CCD 28 through the mirror 11, half mirror 10 anda condensing system 27.

On the other hand, the light beam passed through the objective lens 12is imaged at the position 15, corresponding to the reticle patternposition, and then it is imaged again by the projection optical system16 at a position 17 which is at the wafer side thereof. There is aspherical surface mirror 20 disposed on the stage 19, and the curvatureradius of the spherical mirror 20 is made equal to the distance from theimaging position 17 of the projection optical system. Thus, the lightreflected by the spherical mirror 20 is collected again at the imagingposition 17 of the projection optical system, and it goes again throughthe projection optical system, the objective lens 12, the mirror 11 andthe half mirror 10. The light then passes the condensing system 27, andit is directed to the light receiving surface of the CCD 28. Since thelight beam passing through the projection optical system 16 interfereswith the reference beam as reflected by the final face of the objectivelens 12 as described above, the wavefront of the projection opticalsystem can be measured, on the basis of it. Thus, by analyzing theoutputs of the CCD 28 in a work station 50, annexed to the exposureapparatus, wavefront aberration as well as various aberrations of theprojection optical system 16 such as wavefront aberration and fieldcurvature, for example, causing the wavefront aberration, can bemeasured.

The spherical mirror 20 comprises a concave surface mirror in thisexample. However, a spherical mirror having a convex surface mirror maybe used to provide an interferometer system. On that occasion, thecurvature center position of the convex surface or should be registeredwith the imaging position 17, and the mirror should be placed at anopposite side as compared with the concave surface mirror. As a furtheralternative, a plane surface mirror (or a wafer surface in substitutiontherefor) may be used. On that occasion, with vertex reflection, only arevolutionally symmetrical component of wavefront aberration can bedetected.

Any error in relation to the wavefront which is involved in theinterferometer itself, such as the final face of the objective lens 12or the spherical mirror 20, for example, should be distinguished fromthe wavefront aberration of the projection optical system 16 to beexamined. To this end, it is necessary to measure the wavefrontbeforehand, in accordance with a system error measuring method. Thewavefront of the projection optical system 16 can be measured exactly,by correcting the wavefront error while subtracting it from themeasurement results for the projection optical system 16.

For further enhancement of measurement precision, the measurementthrough the interferometer may be performed in accordance with a fringescan method. The fringe scan can be accomplished by actuating a PZTdevice (not shown) inside the wafer stage 19 to shift the mirror 20 inthe optical axis direction by an amount of about the wavelength, toperform phase modulation of the wavefront. In this connection, movingmeans which is provided for focus adjustment of the projection exposureapparatus may be used as the moving means for moving the sphericalmirror 20 in the optical axis direction.

From the measurement of the wavefront of the projection optical system,information regarding the wavefront aberration at a measurement point isobtainable. Further a revolutionally symmetrical component and arevolutionally asymmetrical component of the wavefront aberration asobtained through the measurement of the wavefront of the projectionoptical system 16 as well as the X-Y-Z coordinates of the objective lens12 and the spherical mirror 20 as obtained from a measuring deviceduring the wavefront measurement may be combined with each other, bywhich interrelationship among the measurement points of the projectionoptical system, can be determined.

The field curvature of the projection optical system can be detected bymeasuring the wavefront of the projection optical system with respect toplural points within the picture plane. More specifically, once thecoordinate position of the detection optical system of theinterferometer upon the wavefront measurement, the wavefront as measuredby the interferometer, and the coordinate position of the sphericalmirror 20 with respect to the optical axis direction of the projectionoptical system 16 are determined, the field curvature can be calculatedfrom the information related to the plural points. The component ofwavefront aberration which is very important in regard to calculation ofthe field curvature is the revolutionally symmetrical power component(defocus component) of the measured wavefront.

Distortion of the projection optical system can also be detected bymeasuring the wavefront of the projection optical system with respect toplural points within the picture plane. More specifically, once thecoordinate position of the detection optical system of theinterferometer upon the wavefront measurement, the wavefront as measuredby the interferometer, and the coordinate position of the sphericalmirror 20 with respect to a direction orthogonal to the optical axis ofthe projection optical system 16 are determined, distortion of theprojection optical system 16 can be calculated from the informationrelated to the plural points. The component of the wavefront aberrationwhich is very important in regard to calculation of distortion is therevolutionally asymmetrical component (tilt component) of the measuredwavefront.

On the basis of the results of measurement, a predetermined lens orlenses of the projection optical system 16 may be displaced, by whichthe aberration of the projection optical system can be adjusted andcontrolled into a desired state.

FIG. 2 is a schematic view of a second embodiment of the presentinvention. Like the first embodiment, in this embodiment, the inventionis applied to an excimer laser stepper having an exposure wavelength of248 nm. In this embodiment, a Twyman-Green type interferometer isprovided on the reticle side.

Denoted at 6 is a light source for the interferometer, from which alight beam of 248 nm corresponding to the second harmonic of an Ar laseris extracted. The laser beam goes via a mirror, a condensing system 7and a pinhole 8. Through an optical system 9, it is transformed into aparallel beam. The parallel light beam is then divided by a half mirror10 to two light beams. The light beam passing through the half mirror 10is reflected by a mirror 29 as a reference beam, and the reflected lightbeam is then reflected by the half mirror 10. After being reflected, thelight beam passes through a condensing system 27 and it impinges on alight receiving surface of a CCD 28.

On the other hand, the light beam reflected by the half mirror 10 goesvia a mirror 11, and it enters an objective lens 13. The light beampassing through the objective lens 13 is once imaged at a position 15corresponding to the reticle pattern position, and then it is re-imagedby the projection optical system 16 at a position 17 on the wafer side.There is a stage 19 on which a spherical surface mirror 20 is mounted.The mirror has a curvature radius which corresponds to the distance fromthe imaging position 17 of the projection optical system. Thus, thelight reflected by the spherical mirror 20 is collected again at theimaging position of the projection optical system. Then, it goes backthrough the projection optical system 16 and passes via the objectivelens 13, the mirror 11, the half mirror 10 and the condensing system 27.Finally, it impinges on the light receiving surface of the CCD 28. Thelight beam passing through the projection optical system 16 interfereswith the reference beam described above, such that the wavefront of theprojection optical system can be measured.

For the correction of a system error in the measured wavefront, use of afringe scan method for enhancement of measurement precision, use of aspherical mirror of a convex surface mirror type, and calculation ofaberrations of the projection optical system may be done in a similarway as in the first embodiment. On the basis of the results of thesemeasurements, a predetermined lens or lenses of the projection opticalsystem 16 may be displaced, by which the aberrations of the projectionoptical system can be adjusted and controlled into a desired state.

FIG. 3 is a schematic view of a third embodiment of the presentinvention. Like the first embodiment, this embodiment is directed to anexcimer laser stepper having an exposure wavelength of 248 nm. In thisembodiment, a radial share type interferometer is provided on thereticle side.

Denoted at 6 is a light source for the interferometer, from which alight beam of 248 nm corresponding to the second harmonic of an Ar laseris extracted. The laser beam goes via a mirror, a condensing system 7and a pinhole 8. Through an optical system 9, it is transformed into aparallel beam. The parallel light beam is then reflected by a halfmirror 10, and it is directed via a mirror 11 to an objective lens 13.The light beam passing through the object lens 13 is imaged at aposition 15 corresponding to the reticle pattern position, and then itis imaged again by the projection optical system 16 at a position 17 onthe wafer side. There is a stage 19 on which a spherical surface mirror20 is mounted. The spherical mirror 20 has curvature radius whichcorresponds to the distance from the imaging position 17 of theprojection optical system. Thus, the light reflected by the sphericalmirror 20 is collected again at the imaging position 17 of theprojection optical system, and it goes back through the projectionoptical system. Then, it advances via the objective lens 13, the mirror11 and the half mirror 10, and it is introduced into an interferometerhaving components denoted by numerals 21-28.

The light beam introduced into the interferometer is divided by a 1:1half mirror 21 into two light beams. The reflected light beam goes via amirror 22 and then it is expanded by a beam expander 23. The expansionmagnification may generally be 10× or more. Because of the expansion,the light beam can be considered as being an approximately idealisticplane wave. Thus, as a reference beam, it is directed to a lightreceiving surface of a CCD 28, via a half mirror 24 and a condensingsystem 27.

On the other hand, the light beam passed through the half mirror 21 goesvia a mirror 25 as a measurement beam, and it is reflected by a halfmirror 24, by which it is combined with the reference beam. The lightbeam is then passed through the condensing system 27 and it is directedonto the light receiving surface of the CCD 28. Here, it is to be notedthat, for fine adjustment of the interferometer, the mirror 25 ismounted on a mechanism 26 by which tilt and parallel eccentricity can beadjusted. The measurement beam described above interfere with thereference beam described above, by which the wavefront of the projectionoptical system 16 can be measured.

For the correction of a system error in the measured wavefront, use of afringe scan method for enhancement of measurement precision, use of aspherical mirror of convex surface mirror type, and calculation ofaberrations of the projection optical system may be done in a similarway as in the first embodiment. On the basis of the results of thesemeasurements, a predetermined lens or lenses of the projection opticalsystem 16 may be displaced, by which the aberrations of the projectionoptical system can be adjusted and controlled into a desired state.

FIG. 4 is a schematic view of a fourth embodiment of the presentinvention. Like the first embodiment, this embodiment is directed to anexcimer laser stepper having an exposure wavelength of 248 nm, wherein aFizeau type interferometer is provided on the wafer side.

Denoted at 6 is a light source for the interferometer, from which alight beam of 248 nm corresponding to the second harmonic of an Ar laseris extracted. The laser beam goes via a mirror, a condensing system 7and pinhole 8. Through an optical system 9, it is transformed into aparallel beam. The parallel light beam then goes via a half mirror 10and a mirror 11, and it enters an objective lens 32. The curvatureradius of the final face of the objective lens 32 on the wafer side ismade equal to the distance to an imaging plane 17 of the projectionoptical system 16 on its wafer side. Thus, reflection light from thatfinal face is directed, as a reference light, to a light receivingsurface of a CCD 28 via a mirror 31, the half mirror 10 and a condensingsystem 27.

On the other hand, the light beam passed through the objective lens 32is imaged upon a plane 17 corresponding to the wafer surface. Then, itis imaged again by the projection optical system 16 upon a plane 15corresponding to the reticle pattern. There is a stage 34 on the reticleside, on which a spherical mirror 33 is mounted. The spherical mirrorhas a curvature radius which is made equal to the distance from theimaging position 15 of the projection optical system, corresponding tothe reticle surface. Thus, the light reflected by the spherical mirror33 is collected again at the imaging position 15 of the projectionoptical system, corresponding to the reticle surface, and then it goesback through the projection optical system 16. Then, it is directed tothe light receiving surface of the CCD 28 via the objective lens 32, themirror 31, the half mirror 10 and the condensing system 27. The lightbeam passed through the projection optical system 16 interferes with thereference beam as reflected by the final face of the objective lens 32as described above, such that the wavefront of the projection opticalsystem 16 can be measured.

Since the detection optical system is provided on the wafer side, byusing the movability of the wafer stage in the X and Y directions,measurement can be done with respect to plural points within the pictureplane of the exposure region. Thus, with the movement of the waferstage, the spherical mirror 33 on the reticle side can be moved by thestage 34 to a predetermined position. Therefore, in addition to thewavefront measurement with respect to the individual measurement points,various wavefront aberrations such as distortion and field curvature,for example, of the projection optical system can be detected, bycalculation, from the measurement data obtained in relation to theplural points.

For the correction of a system error in the measured wavefront, use of afringe scan method for enhancement of measurement precision, andcalculation of aberration of the projection optical system may be donein a similar way as in the first embodiment. Also, a modification ofusing a spherical mirror of a convex surface mirror type on the reticleside, may be made easily. However, in the case of this embodiment, thefringe scan can be accomplished by actuating a PZT device inside thereticle side stage 34 to shift the mirror 33 in the optical axisdirection by an amount of about the wavelength, to cause phasemodification of the wavefront. Alternatively, the fringe scan may beaccomplished by actuating a PZT device inside the wafer stage 19 to movethe objective lens 32 in the optical axis direction by an amount ofabout the wavelength, to cause phase modulation of the wavefront.

On the basis of the results of the measurements, a predetermined lens orlenses of the projection optical system 16 may be displaced, by whichthe aberrations of the projection optical system can be adjusted andcontrolled into a desired state.

FIG. 5 is a schematic view of a fifth embodiment of the presentinvention. Like the first embodiment, this embodiment is directed to anexcimer laser stepper having an exposure wavelength of 248 nm, wherein asingle-path type radial share interferometer is provided on the reticleside.

Denoted at 6 is a light source for the interferometer, from which alight beam of 248 nm corresponding to the second harmonic of an Ar laseris extracted. The laser beam goes via a mirror 11 and enters anobjective lens 13. The light beam passing through the objective lens 13is imaged at a position 17 corresponding to the wafer position, and thenit is imaged again by the projection optical system 16 at a position 15on the reticle side. The light thus imaged at the position 15 advancesvia the objective lens 13, the mirror 11 and a half mirror 10, and it isintroduced into an interferometer having components denoted by numerals21-28.

The light beam introduced into the interferometer is divided by a 1:1half mirror 21 into two light beams. The reflected light beam goes via amirror 22 and then it is expanded by a beam expander 23. The expansionmagnification may generally be 10× or more. Because of the expansion,the light beam can be considered as being an approximately idealisticplane wave. Thus, as a reference beam, it is directed to a lightreceiving surface of a CCD 28, via a half mirror 24 and a condensingsystem 27.

On the other hand, the light beam passed through the half mirror 21 goesvia a mirror 25 as a measurement beam, and it is reflected by a halfmirror 24, by which it is combined with the reference beam. The lightbeam is then passed through the condensing system 27 and it is directedonto the light receiving surface of the CCD 28. Here, it is to be notedthat, for fine adjustment of the interferometer, the mirror 25 ismounted on a mechanism 26 by which tilt and parallel eccentricity can beadjusted. The measurement beam described above interfere with thereference beam described above, by which the wavefront of the projectionoptical system 16 can be measured.

The correction of a system error in the measured wavefront as well ascalculation of aberrations of the projection optical system, forexample, may be done in a similar way as in the first embodiment. On thebasis of the results of these measurements, a predetermined lens orlenses of the projection optical system 16 may be displaced, by whichthe aberrations of the projection optical system can be adjusted andcontrolled into a desire state.

In a case of an i-line stepper, a basic wave of an argon laser having awavelength of 363.8 nm may be used.

In the embodiments of the present invention described hereinbefore, aninterferometer for measurement of an optical performance of a projectionoptical system is mounted on a major assembly of a projection exposureapparatus, by which the wavefront measurement for the projection opticalsystem can be performed on the main assembly of the projection exposureapparatus.

Executing the measurement of an optical characteristic of a projectionoptical system, on the main assembly of a projection exposure apparatus,enables checking the state of the projection optical system as the sameis there. It is, therefore, possible to take any necessary measures inaccordance with the state of the projection optical system.

More specifically, as an example, the aberration state of the projectionoptical system can be corrected in accordance with the result of themeasurement, or a judgment as to whether the operation should beinterrupted or not can be made promptly. As a result of it, the exposureprocess can be performed with the imaging performance of the projectionexposure apparatus held at a high level. This provides a large advantagein the production of semiconductor devices.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

1. A projection exposure apparatus comprising: an illumination opticalsystem for illuminating a pattern of a first object, with use ofexposure light from an exposure light source; a projection opticalsystem for directing the exposure light, emitted from the pattern, ontoa second object; and an interferometer for measuring an opticalcharacteristic of said projection optical system, on the basis of aninterference fringe produced through interference caused between lightemitted from said projection optical system and reference light, whereina light receiving portion of said interferometer for receiving lightemitted from said projection optical system toward the second objectside is provided on a movable stage which carries the second objectthereon.
 2. An apparatus according to claim 1, further comprising meansfor detecting a curvature of field of said projection optical system, byuse of said interferometer.
 3. An apparatus according to claim 1,further comprising means for detecting an aberration of said projectionoptical system, by use of said interferometer.
 4. An apparatus accordingto claim 1, further comprising means for correcting a state ofaberration of said projection optical system, on the basis of themeasurement made by use of said interferometer.
 5. An apparatusaccording to claim 1, further comprising adjusting means for adjustingan amount of aberration of said projection optical system, into adesired state.
 6. An apparatus according to claim 1, further comprisingdriving means for moving an optical element of said projection opticalsystem, on the basis of the measurement made by use of saidinterferometer.
 7. An apparatus according to claim 1, further comprisingmeans for determining whether the operation of said apparatus should bediscontinued, on the basis of the measurement made by use of saidinterferometer.
 8. A device manufacturing method, comprising the stepsof: exposing a workpiece by use of an exposure apparatus as recited inclaim 1; and processing the exposed workpiece.
 9. An apparatus accordingto claim 1, further comprising an interference light source separatefrom the exposure light source, wherein said interferometer uses lightfrom said interference light source.
 10. An apparatus according to claim9, wherein said interference light source is a light source which emitslight having a wavelength of at least one of 496 nm and 363.8 nm.
 11. Anapparatus according to claim 10, wherein said interference light sourceis an argon laser.
 12. An apparatus according to claim 1, wherein thelight receiving portion includes a mirror.
 13. An apparatus according toclaim 12, wherein said mirror is a spherical surface mirror.
 14. Anapparatus according to claim 1, wherein the light receiving portionincludes an objective lens and a mirror.